A broadband panel array antenna includes a polarization layer, a radiating layer and a feed layer which are sequentially stacked from top to bottom. The feed layer is used for converting a single path of TE10 mode signals into a plurality of paths of same-power in-phase TE10 mode signals and transmitting the plurality of paths of TE10 mode signals to the radiating layer. The radiating layer is used for radiating the plurality of paths of TE10 mode signals from the feed layer to a free space. The polarization layer is used for rotating the polarization direction of an electric field generated by the radiating layer to reduce the side lobe in an E-plane direction diagram and an H-plane direction diagram. The broadband panel array antenna has the advantages of being low in side lobe, high in gain and efficiency, and low in machining cost.